The present invention relates generally to the field of road construction equipment and more particularly to a strike-off system and method of manufacture.
Asphalt emulsion based surface treatments such as asphalt slurry and microsurfacing are used to maintain asphalt pavements. The application of such surface treatments extends the life of existing pavements and repairs pavement surface problems such as raveling (loss of aggregate), weathering, wheel path rutting, and loss of roughness or slick wheel paths. The slurry can be mixed by a mobile paving system and applied to the pavement surface in a continuous or batch process. One such mobile paving system is disclosed in U.S. Pat. No. 5,590,976, entitled xe2x80x9cMobile Paving System Using an Aggregate Moisture Sensor and Method of Operation.xe2x80x9d
A mobile paving system can deposit slurry onto a surface through spreader box pulled behind a slurry machine. The ability of the mobile paving system to satisfactorily apply the slurry to the surface can depend upon the ability of the system to evenly distribute the slurry across the full width of the spreader box. Typically a flexible strike-off bar or screed is attached to the spreader box to facilitate generally even distribution of the paving material deposited from the spreader box.
A dual strike-off assembly may be used in which two flexible strike-off bars are positioned behind the spreader box disposed generally parallel to one another. The first strike-off bar may be positioned forward of the second strike-off bar and serve to regulate the amount of paving material deposited on the road surface. The first strike-off bar may be positioned to allow a desired amount of paving material to pass under the first strike-off bar and push forward excess paving material. The second strike-off bar may be positioned to allow the leading edge of the second strike-off bar to contact the road surface in order to smooth and level the deposited paving material to obtain the desire surface texture.
The spreader box width generally determines the width of the road surface that can be treated. Some currently available systems allow operators to expand or contract the spreader box width. The strike-off assembly must similarly adjust in width to facilitate deposition of material along the expanded width of the spreader box. Some currently strike-off systems may automatically expand and contract as the spreader box expands and contracts.
A currently available strike-off assembly may comprise a housing of adjustable length and a flexible screed with a length approximately equal to the maximum width of an expandable spreader box. The housing may lengthen or shorten to match the width of the spreader box. As the housing lengthens it engages the flexible screed. When the housing is lengthened to its maximum length, it may engage the entire length of the flexible screed. When the housing is not expanded to its maximum width, the excess length of the flexible screed can be pulled out of the path of the mobile paving system with flexible tensioning devices. Currently available flexible screeds may provide an elongated molded rubber strip with an asymmetrical cross section. Current flexible screeds are typically molded from a single material and often have a generally L-shaped cross section.
One difficulty with such systems is that molding of flexible strip to obtain suitable geometries is expensive and time consuming. Another difficulty with such systems is that the flexible strip may be housed in a generally hollow housing with an elongated slot. Removal and installation of the flexible member can be time consuming and burdensome, especially when the flexible member and housing are covered with hardened slurry materials. Yet another difficulty with such systems is that an asymmetrical strip is not reversible and only a single side of the strip may be utilized to distribute paving materials.
In accordance with teachings of the present invention, a paving system having a strike-off assembly and method of manufacture are disclosed that provide advantages over previously developed paving systems.
According to one embodiment of the present invention, a mobile paving system with a strike-off assembly for distributing slurry materials onto a road surface is provided. The mobile paving system comprises a mobile paving vehicle with a mixer coupled to the mobile paving vehicle. A spreader box is coupled to the mixer behind the path of the vehicle which distributes paving materials onto the road surface. A strike-off assembly is typically coupled adjacent the spreader box for distributing the surface materials or slurry deposited by the spreader box. The strike-off assembly comprises a screed track and flexible screed which is formed to fit within the screed track.
According to another embodiment of the present invention the mobile paving system further comprises a guide frame coupled to the spreader box. The guide frame may comprise an elongated member with a longitudinal slot extending therethrough and formed to engage the strike-off assembly.
According to another embodiment of the present invention the mobile paving system further comprises a spreader box of expandable width. In this embodiment the guide frame can have a selectively variable length. The guide frame may be coupled tot he spreader box such that as the spreader box expands or contracts the guide frame and the length of the strike-off assembly engaged by the guide frame may expand or contract.
A further embodiment of the present invention is disclosed wherein the screed track and flexible screed are comprised of materials sufficiently flexible to allow the length of the strike-off assembly which is not engaged by the expandable guide frame assembly to be pulled away from the road surface. The screed track comprises a material sufficiently rigid to facilitate its installation and removal into the guide frame.
Yet another embodiment of the present invention is disclosed wherein a secondary guide frame and screed assembly are disposed behind the first guide frame and screed assembly. This preferred embodiment allows an operator to regulate the amount of material deposited onto the road surface with the first screed assembly and use the secondary screed assembly to give the distributed paving material a desired surface texture.
A technical advantage of the present invention is that the screed assembly may be assembled from simple components. The screed track preferably has a generally symmetrical cross section such as a U-shaped bar and the flexible screed may comprise a strip of flexible material cut from a larger sheet of material. It is also a technical advantage that the screed track may be reused with a replacement flexible screed. It is also a technical advantage of the present invention that the flexible screed may be cut along its length to create a fresh leading edge when the leading edge of the flexible screed becomes worn from use.
A further technical advantage of the present invention is the use of material for the screed track which is sufficiently flexible to allow the screed assembly to be pulled away from the road surface and sufficiently rigid to facilitate the installation and removal of the screed assembly into the guide frame.
A further technical advantage of the present invention is that the flexible screed has a generally symmetrical configuration such as a rectangular cross section which allows the flexible screed to be reversed. This allows both faces of the flexible screed to be utilized, extending the life of the screed assembly and reducing the frequency of replacing the flexible screed.
Additional technical advantages of the present invention should be apparent to one of ordinary skill in the art from the description, drawings, and claims.